The cost of manufacturing elastomers in a solution polymerization process is greatly influenced by the cost of isolating the elastomer from the solvent, solvent recovery equipment, and the cost of the solvent used. In addition, practical handling methods dictate that the solution viscosity of the reaction mass be low which in turn limits the polymer concentration obtainable. The unreacted monomers when separated from the polymer during recovery are desirably recycled to the reactor to make the process economical.
It is known that elastomeric polymers can be prepared in a "slurry" process by copolymerizing monomers in a nonsolvent for the polymer such as a halogenated hydrocarbon solvent as disclosed in U.S. Pat. No. 3,291,780, or by copolymerizing the monomers in one or more of the liquid monomers themselves as disclosed in U.S. Pat. Nos. 3,370,052 and 3,358,055. A "slurry" process, particularly one using a liquid monomer reaction medium, has the advantages of requiring a smaller reactor volume throughput per unit of polymer produced than a solution process and a higher reaction rate per unit amount of catalyst. These advantages permit the use of a smaller reactor per unit of polymer produced and mass transfer problems and mixing are minimized because of the lower viscosity of the reaction medium compared to the solution process. In addition, the absence of a solvent eliminates the need for solvent isolation and recycle equipment minimizing the cost for equipment needed for polymer isolation and purification.
Although "slurry" polymerization has many advantages, it does have certain disadvantages. For example, the elastomeric copolymer thus prepared tends to stick to interior reactor walls and surfaces in contact with the reaction medium, thereby fouling the reactor and eventually plugging the connecting lines. Also, the polymer produced usually contains occluded portions of the polymerization medium.
There is a need for a process for carrying out a "slurry" polymerization process for elastomers whereby the elastomer can be removed from the reactor without causing reactor fouling, and the polymer produced is practically free of occluded polymerization medium.